Thick film inks are commonly used in the electronics industry and are of increasing importance as trends progress towards smaller circuits. Thick film circuits are formed by an iterative screen printing process generally involving the deposition of several successive layers of conductor and dielectric inks onto a substrate. Thick film circuits are widely used in electronic devices for the automotive industry and include devices such as electronic power modules for alternators, regulators, and power inverters used for hybrid vehicles. Electronic power modules generate a great deal of heat due to high levels of current and voltage, and thus require materials with high thermal conductivity and diffusivity, while still providing electrical insulation between conductive components.
Direct bonded copper (DBC) substrates are commonly used in power modules due to their high level of thermal conductivity. DBC substrates are composed of a ceramic tile such as alumina or silicon nitride, with a sheet of copper bonded to one or both sides of the ceramic tile. The top copper layer can be pre-formed or etched to form an electrical circuit, while the bottom copper layer remains a solid sheet. The DBC substrate is then soldered to a backplane substrate, typically made of aluminum or other conductive metal, which serves as a heat sink.
While DBC substrates in power modules provide a requisite level of electrical isolation and thermal conductivity, the multiple layers add bulk and complexity. Additionally, the solder joint connecting the DBC substrate to the backplane is a potential failure site, due to the high currents and voltages contributing to joint degradation.